An in-depth summary of Genetic Engineering for IEB matrics. These notes include the roles of important people, a thorough summary of genes and their alleles, how to complete a Punnet square and the role of dominant and recessive genes, sex chromosomes and their diseases, and the methods of genetic ...
GENETIC ENGINEERING
Gregor Mendel
Father of genetics responsible for the first major breakthrough in the study of
heredity by investigating the transfer of characteristic from one generation to
the next
Pea plants had easily observable traits, 7 of which he could manipulate, like plant
height, pod shape, pod colour, flower position, seed colour, seed shape and flower
colour
Mendel cross pollinated parents with certain characteristics
Showed that characteristics are passed from one generation to the next
Discovered the Law of Segregation, Dominance and Independent Assortment
Some facts about genes
Nearly all somatic cells have an exact copy of all the genes in that organism
Because there are 2 of each kind of chromosome (maternal and paternal) each cell
contains two of each kind of gene. These versions are known as alleles.
The gene pool is the set of all genes, or genetic information in a population of sexually
reproducing organisms. A large gene pool indicated high genetic diversity and increased
chance of survival vice versa.
How active are genes?
Each cell contains all genes but only the genes that are needed in that specific cell are
activated, all the other genes are suppressed
Some genes play a role in the early development of the embryo and are inactive
thereafter
Some genes are active in many types of cells, making proteins needed for basic
functions. These are called “housekeeping genes”
A high proportional of our genes are non-coding genes. They do not code for proteins
and occur in between the coding sections. Only about 2% of our genes code for proteins.
How are alleles represented?
A capital letter indicates a dominant allele and a lowercase
represents the recessive allele.
How are alleles passed from parent to offspring?
Alleles are passed by way of chromosomes in the gametes that are
made by the process of meiosis in the sex organs
To sum up:
Somatic cells are diploid as they have:
- A pair of homologous chromosomes
- 2 alleles which may be the same or different
Gametes are haploid as they have:
- 1 pair of homologous chromosomes
, - 1 of each pair of alleles
What happens to the gametes?
During fertilisation a male gamete, with
its alleles fuses with the female
gamete, with its alleles, to form a
diploid zygote.
This divides many times by mitosis to
form an entire new organism made up
of cells, each with the same set of
chromosomes and alleles as in the
zygote.
After fertilisation the zygote, and all the cells that develop from it, will have two alleles
for each gene, one from each parent. These will be in the same locus on each
chromosome of a homologous pair and they may either be homozygous or heterozygous
Genetic diagrams
Genetic diagrams show how characteristics are inherited. They show the gene type and
the phenotype of a cross between 2 parents and help explain why their offspring look
the way that they do.
Generations are shown as follows:
- P1- parent generation
- F1: first filial generation of offspring
- F2: second filial generation of offspring
Alleles are represented as letters. A capital letter for the dominant alleles and a
lowercase for the recessive.
Punnett square
A Punnett square is a way to represent a cross between 2 organisms for any number of
characteristics for which the parental genotypes are known
It predicts the probability of an offspring’s genotype and phenotype
However, these ratios are likely to be achieved only when many offspring are produced
How to answer a Punnett square question
P1: Bb x Bb
F1:
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